Cannot hear audio clips in Final Cut Pro

I was editing my video when suddenly, some audio clips did not have any audio. The waveforms disappeared and I cannot hear some of these audio clips.

Here is everything that I have tried doing without any success

• I have checked the volume and my speakers and they are all working fine.
• I restarted Final Cut Pro multiple times.
• I have turned on and off the reference waveforms to see if that makes any difference.

This has happened to me a few times already but I'm not sure how I managed to fix it back then. I can't recall what was the last thing I did before this happened but I would appreciate any help or advice. Thanks.